ES3038198T3 - Barrier-coated cellulose-based substrate, laminated packaging material and packaging container comprising the cellulose-based substrate - Google Patents

Abstract

The present invention relates to barrier-coated cellulosic substrates (10; 25a; 25b) and a method for manufacturing them by dispersion coating with a barrier pre-coating (13) and subsequent vapor deposition coating with a barrier deposition coating (14). The invention also relates to laminated packaging materials (20a; 20b) comprising the barrier-coated cellulosic substrates (10), particularly for food packaging in liquid cartons, and to liquid cartons comprising the laminated packaging material.

Description

DESCRIPTION

Cellulose-based substrate coated with a barrier, layered packaging material, and packaging container comprising the cellulose-based substrate

Technical field

The present invention relates to barrier-coated paper or cellulose-based substrates and a method for manufacturing them by dispersion coating with a barrier pre-coating and subsequent vapor deposition coating with a barrier coating. The invention further relates to laminated packaging materials comprising these barrier-coated paper or cellulose-based substrates, particularly for packaging liquid foods in Tetra Pak cartons, and to Tetra Pak-type liquid packaging containers comprising the laminated packaging material.

Background of the invention

Single-use, disposable packaging containers for liquid foods are often produced from a cardboard-based or Tetra Pak-type packaging laminate. One such commonly used packaging container is marketed under the Tetra Brik Aseptic® brand and is primarily used for the aseptic packaging of liquid foods such as milk, fruit juices, etc., sold for long-term storage under ambient conditions. The packaging material in this type of container is typically a laminate comprising a main or core layer of paper, cardboard, or other cellulose-based material, and outer liquid-tight layers of thermoplastic materials. To make the packaging container gas-tight, particularly oxygen-tight, for example, for aseptic packaging or packaging of milk or fruit juice, the laminate in these containers usually includes at least one additional layer, most commonly aluminum foil.

On the inside of the laminate, that is, the side facing the food contents of a container made from the laminate, is the innermost layer, applied over the aluminum foil. This innermost layer may consist of one or more partial layers comprising heat-sealable thermoplastic polymers, such as adhesive polymers and/or polyolefins. In addition, on the outer surface of the main layer, there is an outermost heat-sealable polymer layer.

Packaging containers are generally produced using modern, high-speed packaging machines that form, load, and seal containers from a strip or from prefabricated blanks of packaging material. Packaging containers can be produced by reforming a strip of laminated packaging material into a tube by joining the two longitudinal edges of the strip together with an overlapping seam, welding the innermost and outermost layers of heat-sealable thermoplastic polymer together. The tube is then filled with the intended liquid food product and subsequently divided into individual containers by repeated transverse seals of the tube at predetermined intervals below the level of the contents. The containers are separated from the tube by slits along the transverse seals and given the desired geometric shape, typically a parallelepiped, by forming folds along crease lines in the packaging material.

The main advantage of this continuous tube-forming, filling, and sealing packaging method is that the band can be continuously sterilized just before tube formation. This enables aseptic packaging, meaning that both the liquid contents and the packaging material are kept free of bacteria, and the filled container is produced under clean conditions. This allows for extended storage, even at room temperature, without the risk of microbial growth in the product. Another significant advantage of the Tetra Brik® packaging method, as mentioned earlier, is the possibility of high-speed continuous packaging, which has a positive impact on cost-effectiveness.

Packaging containers for sensitive liquid foods, such as milk or juice, can also be produced from sheet blanks or prefabricated blanks of the laminated packaging material of the invention. Starting with a tubular blank of the laminated packaging material that is folded flat, containers are produced by first constructing the blank into an open tubular capsule, one end of which is closed by folding and heat-sealing integral end panels. The closed capsule is then filled with the food product in question, e.g., juice, through its open end, which is subsequently closed by further folding and heat-sealing of the corresponding integral end panels. An example of a packaging container produced from sheet and tubular blanks is the so-called conventional gable-lid container. Containers of this type with a molded top and/or a screw-on lid made of plastic are also available.

A layer of aluminum foil in packaging laminate provides gas barrier properties significantly superior to most other gas barrier materials. Conventional aluminum foil-based packaging laminate for aseptic packaging of liquid foods is still the most economical packaging material, at its performance level, currently available on the market.

Any other material that competes with metallized paper-based materials must be economical in terms of raw materials, have comparable food preservation properties, and have a comparably low complexity in converting the materials into a finished packaging laminate.

Among the efforts to develop metallized paper materials other than aluminum for packaging liquid foods in Tetra Pak, there is also a general incentive towards the development of prefabricated films or sheets that have high and multiple barrier functionalities, which can replace the aluminum foil barrier material in conventional laminated packaging material, or combine several separate barrier layers in the laminated material, and adapt it to conventional procedures for lamination and manufacturing.

Preferred types of this more environmentally sustainable alternative barrier material are barrier-coated paper substrates produced by aqueous dispersion coating or vapor deposition coating onto thin paper carrier substrates. Various aqueous dispersion coating and vapor deposition coating procedures and material formulations exist for these coatings, and there is a need for cost-effective, non-metallized (i.e., aluminum-free) barrier materials of this type that have improved barrier properties for use in packaging laminates for liquid food packaging, particularly against gases such as oxygen.

A prior patent publication WO2011/003565A1 discloses an aluminum foil-free packaging material comprising a pre-coated and metallized Kraft paper substrate for the purpose of inducing heat sealing. It recommends fairly thick coating layers and the inclusion of additional nanoclay particles in the pre-coating. For good gas barrier properties, additional barrier coating layers should also be applied to the packaging laminate, such as on the back face of the paper substrate or on the main cardboard layer. These additional barrier coatings would be necessary in this disclosure to supplement the rather low barrier properties provided by the metallized Kraft paper.

Prior patent publication WO2017/089508A1 discloses how additional enhanced barrier properties can be obtained from a metallized paper in a similar packaging laminate by selecting a paper substrate that provides optimal properties. This metallized paper substrate provided not only enhanced barrier properties but also improved stability of the metallized layer for the purpose of inducing heat sealability. Prior patent publication WO2012/093036A1 discloses another example of a barrier-coated cellulose-based substrate for packaging applications without the pre-coating of the base layer.

However, there remains a need for additional improved gaseous oxygen barrier properties from barrier-coated paper and other cellulose-based substrates. There also remains a need for improved recyclability and sustainability properties of the materials used.

Disclosure of the invention

Accordingly, one objective of the present invention is to provide improved barrier-coated paper or cellulose-based substrates for layering in packaging materials.

It is also a general objective of the invention to provide barrier-coated paper or cellulose-based substrates that have good barrier properties as well as improved recyclability and sustainability that meet the needs of future sustainable tetrabrik-type liquid laminated packaging materials.

An additional general objective of the invention is to provide packaging materials for oxygen-sensitive products, such as non-metallized laminated packaging materials for liquid, semi-solid, or moist food products, that do not contain aluminum foil but still have good gas barrier properties and other properties suitable for long-term aseptic packaging at a reasonable cost.

A particular objective is to provide an economical non-metallized paper or cardboard-based laminated packaging material, relative to aluminum foil barrier materials, that has good barrier properties for gases and water vapor, as well as recyclability and a sustainable environmental profile in order to manufacture packaging for long-term aseptic food storage.

A further objective of the invention is to provide a mechanically robust, heat-sealable packaging laminate based on inexpensive non-metallized paper or cardboard that has good barrier properties for gases and water vapor and good internal adhesion between its layers, in order to manufacture aseptic packaging containers for the long-term storage of liquid foods with nutritional quality maintained under ambient conditions.

These objectives can thus be achieved according to the present invention by means of the barrier-coated paper or cellulose-based substrate, the laminated packaging material, the packaging container, and the method of manufacturing the packaging material, as defined in the appended claims.

Summary of the invention

According to a first aspect of the invention, a barrier-coated cellulose-based substrate for use as a barrier film in a layered packaging material for liquid food products comprises a cellulose-based substrate and, applied onto a first top layer of the cellulose-based substrate, a barrier pre-coating applied by means of a dispersion or solution coating, and, furthermore, on the barrier pre-coating, a barrier coating applied by vapor deposition, wherein the barrier-coated cellulose-based substrate further comprises a base-layer pre-coating, which is different from the barrier pre-coating and is applied by means of a dispersion or solution coating, onto the cellulose-based substrate and is directly adjacent to and in contact with the first top surface of the cellulose-based substrate layer, and is located below the barrier pre-coating, the barrier-coated cellulose-based substrate being thus suitable for providing barrier properties to gases and water vapor in This laminated packaging material and containers made from it.

In one embodiment, the barrier pre-coating comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of poly(vinyl alcohol), PVOH and ethylene vinyl alcohol, EVOH, and the barrier deposition coating is a vapor deposition coating, such as from a material selected from metals, metal oxides, inorganic oxides and carbon coatings.

In a further embodiment, the barrier deposition coating is a vapor deposition coating selected from the group consisting of an aluminum metallization coating, and aluminum oxide, AlOx, and preferably is an aluminum metallization coating.

According to a second aspect of the invention, a layered packaging material is provided comprising the barrier-coated cellulose-based substrate of the invention. The layered packaging material may further comprise a first outer liquid-tight, heat-sealable polyolefin layer and a second inner liquid-tight, heat-sealable polyolefin layer.

For the purpose of packaging liquid food products in tetrabrik cartons, the laminated packaging material may further comprise a main layer of paper or cardboard or other cellulose-based material, an outermost first liquid-tight heat-sealable polyolefin layer, an innermost second liquid-tight heat-sealable polyolefin layer, and, disposed on the inner face of the main paper or cardboard layer, between the main layer and the innermost layer, the barrier-coated cellulose-based substrate.

In a third aspect of the invention, a packaging container comprising the layered packaging material of the invention is provided, intended for packaging a liquid, semi-solid, or moist food. According to one embodiment, the packaging container is at least partially made of the layered packaging material of the invention, and according to a further embodiment, it is entirely made of the layered packaging material.

In a fourth aspect of the invention, a method is provided for manufacturing a barrier-coated cellulose-based substrate, comprising a first step of providing a cellulose-based substrate as a mobile web in a roll-to-roll system, a second step of applying a first dispersion or solution of a base-layer pre-coating composition onto the mobile cellulose-based substrate, and subsequently drying the applied base layer by forced evaporation, a third step of applying a second dispersion or solution of a barrier pre-coating composition, having ingredients different from the base-layer pre-coating composition, onto the mobile cellulose-based substrate coated with the base layer, and subsequently drying the applied barrier pre-coating by forced evaporation, and a fourth step of further depositing, onto the barrier pre-coating on the mobile barrier-pre-coated cellulose-based substrate, a barrier coating by vapor deposition coating operation.

While it has been assumed until now that the improved gas barrier properties of these barrier-coated papers can be achieved by using better cellulose-based substrates, which inherently provide gas barrier properties when further layered with polymer layers, or by coating more polymer with inherent gas barrier properties in thicker layers, it has recently become better understood that the surface portion of the cellulose-based substrate plays a key role in the optimal performance of subsequently applied coatings that provide gas barrier properties. Therefore, it can be achieved by adding an additional base coat pre-coating over the cellulose-based substrate and then applying the barrier coatings. It has been observed that the barrier qualities of the cellulose-based substrate itself do not need to be as high, and the amount of gas barrier polymer used as a barrier pre-coating can even be reduced. The resulting barrier in a laminated packaging will still be very high if such a base coat pre-coat is used, even though it does not itself contribute inherent barrier properties. The composition of the base coat pre-coat must be selected to provide a homogeneous, uniform, and compatible surface to receive the gas barrier pre-coat with additional dispersion, which in the next stage will receive an additional vapor deposition barrier coating. However, the material selected for the base coat pre-coat does not need to contribute inherent gas barrier properties.

The base coat pre-coating material advantageously comprises a polymer selected from the group consisting of starch, modified starch, and cellulose ethers.

Thus, the barrier-coated cellulose-based substrate obtained by the above method and the configuration of the coating layers provides improved barrier properties to a layered packaging material comprising it, and may also give it an improved recyclability and sustainability profile.

Detailed description

By the term "long-term storage", as used in connection with the present invention, it is understood that the packaging container must be able to preserve the qualities of the packaged food product, i.e., nutritional value, hygienic safety and flavor, under ambient conditions for at least 1 or 2 months, such as at least 3 months, preferably longer, such as 6 months, such as 12 months, or more.

The term "packaging integrity" generally refers to the airtightness of the packaging, that is, its resistance to leaks or breakage. This term also encompasses the packaging's resistance to the entry of microbes, such as bacteria, dirt, and other substances that can spoil the food product inside and shorten the expected shelf life of the packaging.

A significant contribution to the integrity of a laminated packaging material comes from good internal adhesion between adjacent layers. Another contribution comes from the material's resistance to defects, such as pores, cracks, and the like, within each layer. Yet another contribution comes from the strength of the sealing joints, which seal the material to itself when forming a packaging container. With regard to the laminated packaging material itself, the integrity property thus focuses primarily on the adhesion of the respective layers to their adjacent layers, as well as the quality of the individual layers. Regarding the sealing of the containers, integrity focuses primarily on the quality of the sealing joints, which is ensured by the smooth and robust operation of the filling machines. This, in turn, is ensured by appropriately matched heat-sealing properties of the laminated packaging material.

The term "liquid or semi-liquid food" generally refers to food products that have a fluid content and may optionally contain pieces of food. Dairy products and milk, soy, rice, cereals and seed drinks, juice, nectar, still drinks, energy drinks, sports drinks, coffee or tea drinks, coconut water, wine, soups, jalapeños, tomatoes, sauces (such as pasta sauce), beans, and olive oil are some, but not limited to, examples of food products considered.

The term "aseptic" in relation to packaging material and a packaging container refers to conditions in which microorganisms are eliminated, deactivated, or destroyed. Examples of microorganisms include bacteria and spores. An aseptic procedure is generally used when a product is aseptically packaged in a packaging container. For continued asepsis throughout the container's shelf life, the integrity properties of the container are, of course, very important. For the long-term shelf life of a contained food product, it may also be important that the container have barrier properties against gases and vapors, such as gaseous oxygen, in order to maintain its original flavor and nutritional value, such as its vitamin C content.

The term "main layer" normally refers to the thickest layer or the layer containing the majority of the material in a multi-layered laminate; that is, the layer that contributes most to the mechanical properties and dimensional stability of the laminate and of packaging containers folded from it, such as cardboard or a Tetra Pak. It can also mean a layer that provides a greater thickness span in a sandwich structure, which further interacts with opposing stabilizing layers, having a higher Young's modulus, on each face of the main layer, in order to achieve sufficient mechanical properties and dimensional stability.

Thickness measurements were performed using transmission electron microscopy with a Titan 80-300 instrument, FEI. Samples can be prepared by ultramicrotomy on a Leica EM UC6 microtome.

OTR was measured using an Oxtran 2/21 (Mocon) device based on coulometric sensors.

The method for determining OTR identified the amount of oxygen per unit area and time when passing a material through a defined temperature, a given atmospheric pressure, for a certain time, that is, in an atmosphere of 100% oxygen, for 24 hours.

Water vapor transmission rate (WVTR) measurements were performed using a Permatran 3/33 (Mocon) instrument (standard: ASTM F1249-13 using a modulated infrared sensor for relative humidity detection and WVTR measurement) at 38°C and 90% drive force.

The suitable substrate for barrier coatings according to the invention is not limited to a certain type of paper, but also includes other cellulose-based substrates, based on any type of natural, fibrous, or fibrillar cellulose. However, the invention is not applicable to plastic or polymer substrates, such as films made from regenerated cellulose.

Until now, it appears that papers or cellulose-based substrates with a Bendtsen smoothness of 200 ml/min or less, such as approximately 150 ml/min or less, on their coating face ("top face" or "printed face"), can provide particularly good barrier coating structures according to the present invention, from an oxygen barrier point of view. However, it is also perceived that the novel combination of pre-coatings and barrier coating of the present invention can improve the barrier properties of virtually any paper substrate beyond what was previously thought possible.

To be suitable for the final barrier coating stage using a vapor deposition coating process, the substrate needs to be thin, such as 60 g/m² or less, 50 g/m² or less, preferably 45 g/m² or less, and most preferably 40 g/m² or less, for reasons of production efficiency and economy, and to prevent blistering of the coating due to air entrapment in a porous, fibrous, cellulose-based substrate. Furthermore, thinner cellulose-based substrates or those with a basis weight of less than 30 g/m² can be too weak mechanically and/or less dimensionally stable when coated with wet dispersions and subsequently dried, resulting in shrinkage or warping problems. Therefore, papers with a basis weight of 30 to 50 g/m², and most preferably 35 to 45 g/m², are preferred.

For optimal barrier properties using a minimal amount of barrier material, it has been observed that a barrier coating applied by deposition, intended only to a nanometer thickness, requires a thin pre-coating made from a gas barrier polymer when applied to a paper or cellulose-based substrate. The best working barrier pre-coating is selected from vinyl alcohol polymers and copolymers, which have inherent gas barrier properties and are food-safe and environmentally sustainable in terms of both recyclability and industrial coating and layering processes. These polymers are water-dispersible and/or water-soluble and can be applied by an aqueous dispersion coating process, also known as a liquid film coating process. Non-aqueous or only partially aqueous coating compositions, such as those based on alcohols or mixtures of alcohol and water, could also be suitable for achieving the desired results of this invention. However, they are likely to be less suitable from an environmental sustainability perspective.

Suitable procedures for coating low-dry-matter polymer dispersion/solution compositions are broadly any suitable wet coating method, such as gravure roller coating, air spraying, airless spraying, reverse roller coating, wire rod coating, groove coating, air sheet coating, curtain flow coating, spray coating, dip coating, and brush coating. Experiments for the present invention were carried out by gravure coating, but it is believed that any of the above liquid film coating methods that contribute to generating a smooth and uniform coated surface would be suitable for carrying out the invention.

The preferred barrier pre-coating compositions are thus based on the two most common types of polymers and copolymers suitable for dispersion coating, based on vinyl alcohol monomers, i.e., poly(vinyl alcohol) (PVOH) and ethylene-vinyl alcohol (EVOH).

Preferably, the gas barrier polymer is PVOH, because it provides good film-forming properties, gas barrier properties, economy, food compatibility, and odor barrier properties.

A PVOH-based gas barrier composition performs best when the PVOH has a saponification degree of at least 98%, preferably at least 99%, although PVOH with lower saponification degrees will also provide oxygen barrier properties. Furthermore, EVOH can be advantageous in providing some moisture resistance to the barrier material, as the copolymer comprises ethylene monomer units. The amount depends on the choice of EVOH grade, but this will come at the expense of some of the material's inherent oxygen barrier properties compared to PVOH alone. Conventional EVOH polymers are typically intended for extrusion and cannot be dispersed or dissolved in an aqueous medium to produce a thin, liquid-film coated barrier film of 3.5 g/m² or less. EVOH is believed to require a relatively high proportion of vinyl alcohol monomer units to be water-dispersible, and its properties should be as close as possible to those of liquid film coating PVOH grades. Therefore, an extruded EVOH coating is not a viable alternative to liquid film coating EVOH because it inherently has properties less similar to PVOH than extrusion coating EVOH grades, and because it cannot be economically applied in quantities below 4 g/m² as a single layer using extrusion coating or extrusion lamination.

The barrier pre-coating composition may also comprise approximately 1 to approximately 20 wt% of an inorganic laminar composite based on the weight of the dry coating, such as exfoliated nanoclay particles, such as bentonite. Thus, the barrier layer may include approximately 99 to approximately 80 wt% of the polymer based on the weight of the dry coating. An additive, such as a dispersion stabilizer or the like, may also be included in the gas barrier composition, preferably in an amount of no more than approximately 1 wt% based on the weight of the dry coating. The total dry content of the composition is preferably 5 to 15 wt%, more preferably 7 to 12 wt%.

A possible additional additive in the barrier pre-coating composition may be a polymer or compound with carboxylic acid functional groups to enhance the water vapor and oxygen barrier properties of a PVOH coating. Suitablely, this polymer with carboxylic acid functional groups is selected from ethylene-acrylic acid (EAA) copolymer and ethylene-methacrylic acid (EMAA) copolymers, or a mixture thereof. In one embodiment, this barrier layer mixture may consist essentially of PVOH, EAA, and an inorganic layer compound. The EAA copolymer may be included in the barrier layer in an amount of approximately 1–20% by weight, based on the weight of the dry coating.

It is believed that some additional improved oxygen and water barrier properties can result from an esterification reaction between PVOH and EAA at an increased drying temperature, whereby the PVOH becomes crosslinked by hydrophobic EAA polymer chains, which are thus incorporated into the PVOH structure. Crosslinking can alternatively be induced by the presence of polyvalent compounds, e.g., metallic compounds such as metal oxides. However, these mixtures are more expensive due to the cost of the additives and may be less preferable from a recyclability standpoint.

Thus, although it is preferable to use a barrier precoat of a composition of pure PVOH or EVOH, advantageous gas barrier results can also be obtained with barrier precoats comprising additional additives as described above.

A barrier pre-coating can be applied at a total rate of 0.1 to 3 g/m², preferably 0.5 to 2 g/m², dry weight. Below 0.1 g/m², no gas barrier properties will be achieved at all, while above 3 g/m², the pre-coating will not contribute to cost savings in the packaging lamination due to the high cost of barrier polymers in general and the high energy cost of liquid evaporation. A noticeable level of oxygen barrier is achieved with PVOH at 0.5 g/m² and above, and a good balance between barrier properties and cost is achieved between 0.5 and 2 g/m².

In one embodiment, the barrier pre-coating can be applied in two consecutive stages with intermediate drying, as two-part coats. When applied as two-part coats, each coat is applied in quantities of 0.1 to 2 g/m², preferably 0.5 to 1.5 g/m², and provides a total layer of superior quality barrier composition for liquids and gases. More preferably, the two-part coats are applied in quantities of 0.5 to 1 g/m² each.

In one embodiment, the barrier pre-coating has been applied by means of a dispersion or solution coating in an amount of 0.5 to 2 g/m2, preferably 0.5 to 1.5 g/m2, on a dry weight basis.

For an unexpected improvement of the invention, the barrier precoat should not be applied directly onto the paper or cellulose-based substrate, but should be preceded by a first basecoat precoat of a different polymer and composition, to prepare the substrate surface for the barrier precoat. It is not fully understood why, i.e., which physical and/or chemical conditions at the interface between the two precoats are the primary factor in the improvement of the resulting barrier properties, but it is believed that the particular properties of aqueous starch compositions promote a dense and uniform basecoat surface for further coating and compatible adhesion chemistry and weldability for the subsequent application of a poly(vinyl alcohol)-based barrier precoat.

The base layer pre-coating must be coated directly onto, and adjacent to, the paper or cellulose-based substrate. The paper allows moisture to migrate outward through the laminated packaging material, and the base layer pre-coating material also permits this water vapor migration. Thus, there will be no unfavorable moisture entrapment near the moisture-sensitive PVOH or EVOH barrier pre-coating. Any moisture migration through the material from the liquid food product inside the package will simply be further transported through the paper and the cardboard main layer of the laminated packaging material to the outside of the packaging container. The cellulose-based substrate and the cardboard main layer "breathe" the moisture from the barrier pre-coating and thus maintain the moisture content within the barrier pre-coating substantially constant over time.

For the aforementioned functions of layer smoothing, moisture transport, and surface compatibility, the base coat pre-coat preferably comprises a polymer selected from the group consisting of starch, modified starch, and cellulose ethers. These polysaccharide compounds have similar properties in this regard and all will provide the same advantages.

More specifically, the base coat pre-coating may comprise a material selected from the group consisting of starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), and sodium carboxymethylcellulose (NaCMC). These natural, plant-based compounds will provide optimal desired effects in line with the above, and also with regard to ease of recycling and sustainability.

Suitable starch materials, or starch derivatives, can be oxidized starch, cationic starch, or hydroxypropylated starch. Examples of modified starches are potato starch oxidized with hypochlorite (Raisamyl 306 from Raisio) and hydroxypropylated corn starch (Cerestar 05773); however, other forms of starch can also provide the desired properties in a basecoat pre-coat.

Furthermore, since this basecoat pre-coat allows for a reduction in the amount of barrier pre-coat while still achieving the same level of barrier properties, a slightly higher level of sustainability can be achieved, as the preferred basecoat pre-coat compounds can be almost entirely plant-based. A basecoat pre-coat composition of natural starch, for example, would be 100% plant-based and 0% fossil-based.

In one embodiment, the total amount applied of the base coat pre-coat and the barrier pre-coat is approximately 1 to approximately 4 g/m2, preferably 1.5 to approximately 3 g/m2, on a dry weight basis.

In a further embodiment, the base coat pre-coating has been applied by means of a dispersion coating or aqueous solution in an amount of 0.5 to 2 g/m2, preferably 0.5 to 1.5 g/m2, on a dry weight basis.

The vapor-deposited barrier coating, which is then coated onto the surface of the barrier pre-coating, is applied by means of physical vapor deposition (PVD) or chemical vapor deposition (CVD), for example by plasma-enhanced chemical vapor deposition (PECVD).

In one embodiment, the vapor deposition coating is made of a material selected from metals, metal oxides, inorganic oxides, and carbon coatings.

In a further embodiment, the barrier deposition coating is a vapor deposition coating selected from the group consisting of an aluminum metallization coating, and aluminum oxide, AlOx, and preferably is an aluminum metallization coating.

These thin vapor-deposited coating layers are nanometric in thickness, that is, they have a thickness that is most appropriately measured in nanometers, for example from 5 to 500 nm (50 to 5000 Å), such as from 5 to 200 nm, such as from 5 to 100 nm, such as from 5 to 50 nm.

Generally, below 5 nm the barrier properties may be too low to be useful, and above 200 nm, as well as above 100 nm, as well as above 50 nm, depending on the type of vapor deposition coating, the barrier coating may be less flexible and thus more prone to cracking when applied over a flexible substrate, and would also be more expensive.

In one embodiment, the barrier deposition coating is applied to a thickness of 10 to 80 nm, such as 10 to 50 nm, such as 10 to 45 nm.

A common type of vapor deposition coating, which often has some barrier properties, particularly water vapor barrier properties, are so-called metallization coatings, e.g., physical vapor deposition coatings of metallic aluminum.

This vapor-deposited layer, consisting substantially of metallic aluminum, can be 5 to 50 nm thick, more preferably 5–40 nm, which corresponds to less than 1% of the metallic aluminum material present in a standard-thickness aluminum foil used for packaging, i.e., 6.3 g/m². Although vapor-deposited metallic coatings require significantly less metallic material, they provide only a low level of oxygen barrier properties at best and need to be combined with an additional gas barrier material to provide a final layered material with sufficient barrier properties. Furthermore, it can complement an additional gas barrier layer, which does not have water vapor barrier properties but is quite sensitive to moisture.

Other examples of vapor deposition coatings include aluminum oxide (AlOx, AbOa) and silicon oxide (SiOx) coatings. Generally, these PVD coatings are more brittle and less suitable for layering in packaging materials, while metallized layers, as an exception, do possess mechanical properties suitable for layering despite being made of PVD.

Typically, an aluminum-metallized layer inherently has a thin surface portion consisting of aluminum oxide due to the nature of the metallization coating procedure used.

In one embodiment, this aluminum-metallized layer has been applied to an optical density (OD) of 1.8 to 2.5, preferably 1.9 to 2.2. At an optical density lower than 1.8, the barrier properties of the metallized film may be too low. Above 2.5, on the other hand, the metallization layer becomes brittle, and the thermal stability during the metallization process will be low due to a higher thermal load when the substrate film is metallized for a longer period. The quality and adhesion of the coating may then be negatively affected. The optical density is measured in production using a densitometer, i.e., an instrument (such as a Macbeth, Tobias, or similar) that uses the principle of diffuse light transmission. The instrument is suitable for measuring the optical density values of films coated with aluminum metallization. The accuracy and precision of the measurements is high and approximately +- 0.2 OD and approximately +-0.01 OD, respectively, with a measurement range of 0 to 6.60 OD.

In laboratory measurements, a spectrophotometer can alternatively measure light transmission across the entire visible spectrum (380-800 nm). Optical density is calculated from the light transmission value (T) at 560 nm, according to the formula OD = -log10 (h/lü), and the values obtained are equally accurate (+/- 0.2 OD) and comparable to desitometric light transmission values.

Other coatings can be applied using a plasma-enhanced chemical vapor deposition (PECVD) method, where a vapor of a compound is deposited onto the substrate under more or less oxidizing conditions. Silicon oxide (SiOx) coatings, for example, can also be applied using a PECVD procedure, and very good barrier properties can then be obtained under certain coating conditions and gas formulations.

DLC defines a class of amorphous carbonaceous material (diamond carbon) that exhibits some of the typical properties of diamond. Preferably, a hydrocarbon gas, such as acetylene or methane, is used as the processing gas in a plasma to produce an amorphous hydrogenated carbon barrier layer coating by a vacuum PECVD process, i.e., DLC. DLC coatings applied by vacuum PECVD provide good adhesion to adjacent polymer or adhesive layers in a layered packaging material. Particularly good adhesion to adjacent polymer layers is obtained with polyolefins, and in particular with polyethylene and polyethylene-based copolymers.

The vapor deposition barrier coating is preferably applied by vacuum vapor deposition, but it could also be applied, less preferably, by other methods generally known in the art, although these methods have lower productivity and lower coating quality, such as electroplating or sputtering. The most preferred metal according to the present invention is aluminum, although any other metal that can be vacuum deposited, electroplated, or sputtered may be used. Thus, less common metals such as Au, Ag, Cr, Zn, Ti, or Cu are less preferred alternatives. Generally, thin coatings of metal or a mixture of metal and metal oxide provide barrier properties against water vapor and are used when the desired function is to prevent water vapor from migrating into and through the multilayer film or packaging laminate. Preferably, for the purpose of manufacturing food packaging materials, the metal in a metallization or inorganic metal coating is aluminum (Al).

The barrier-coated paper or cellulose-based substrate obtained by the above method provides excellent low OTR and low WVTR and is suitable for lamination in a laminated packaging material and also for folding and sealing operations of this laminated material into packaging.

The layered packaging material comprising the barrier-coated cellulose-based substrate further comprises a first outer protective layer (22a; 22b) and a second inner liquid-tight heat-sealable layer (23a; 23b; 23b'). The second inner liquid-tight heat-sealable layer (23a; 23b; 23b') may comprise or be made of a polyolefin polymer. The first outer protective layer may be transparent to allow visibility of a decorative pattern printed on the outer surface of the main layer. It may also comprise or be made of a polyolefin polymer.

A layered packaging material based on a tetrabrik for packaging liquid food may thus comprise a main layer of paper or cardboard, a first outer protective layer, a second inner liquid-tight heat-sealable layer, and, disposed on the inner face of the main paper or cardboard layer, towards the inside of a packaging container made of the packaging material, between the main layer and the second inner liquid-tight heat-sealable layer, said paper or cellulose-based substrate coated with a barrier.

The layered packaging material based on a tetrabrik may comprise a main layer of paper or cardboard, an outermost first liquid-tight heat-sealable polyolefin layer, an innermost second liquid-tight heat-sealable polyolefin layer, and, disposed on the inner face of the main layer of paper or cardboard, towards the inside of a packaging container made of the packaging material, between the main layer and the innermost layer, said barrier-coated paper or cellulose-based substrate.

A main layer of paper or cardboard for use in the invention typically has a thickness of approximately 100 pm to approximately 600 pm, and a weight per unit area of approximately 100-500 g/m2, preferably approximately 200-300 g/m2, and can be a conventional paper or cardboard of suitable packaging quality.

For the long-term, cost-effective aseptic packaging of a liquid food product, a thinner packaging laminate with a thinner core layer can be used. Packaging containers made from these laminates are not formed by folding and are more similar to flexible pillow pouches. Suitable paper for these pouches typically has a weight per unit area of approximately 50 to approximately 140 g/m², preferably approximately 70 to approximately 120 g/m², and more preferably 70 to approximately 110 g/m². Since the barrier-coated substrate in this invention can itself contribute some stability to the laminated material, the paper layer corresponding to a "core" layer can be even thinner and interact with the barrier cellulose-based substrate in a sandwich-like interaction to still produce a laminated packaging material that, together, has the desired mechanical properties.

The barrier-coated paper or cellulose-based substrate may be bonded to the main layer by an intermediate bonding layer of adhesive or thermoplastic polymer, thereby bonding the uncoated surface of the barrier-coated paper to the main layer. According to one embodiment, the bonding layer is a polyolefin layer, such as, in particular, a polyethylene-based polyolefin copolymer layer or a combination thereof, which includes, in most cases, ethylene monomer units. The bonding layer may be bonded to the barrier-coated cellulose-based substrate by melt extrusion, layering the polymer bonding layer between a strip of the main layer and a strip of the cellulose-based substrate, and simultaneously pressing the three layers together as it is advanced through the contact line of the layering rollers, thereby providing a layered structure by extrusion layering.

In another embodiment, the barrier-coated cellulose-based substrate can be bonded to the main layer by wet-applying an aqueous dispersion of an adhesive composition comprising a polymeric adhesive binder to one of the surfaces of the web to be laminated, and pressing the two paper webs together as they advance through the contact line of the lamination rollers, thereby providing a laminated structure by wet lamination. The moisture from the aqueous adhesive composition is absorbed into the fibrous cellulose network of the two paper layers and partially evaporates over time during subsequent lamination procedures. There is no need for a forced drying step. The polymeric adhesive binder is selected from the group consisting of acrylic polymers and copolymers, cellulose derivatives and polysaccharides, vinyl acetate polymers and copolymers, and vinyl alcohol. For the best possible environmental and sustainability profile, adhesive binders derived from plant or non-fossil sources are preferred.

Suitable thermoplastics for the outermost and innermost liquid-tight heat-sealable layers are polyolefins such as homo- and copolymers of polyethylene and polypropylene, preferably polyethylenes and more preferably polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear LDPE (LLDPE), single-site metallocene catalyst polyethylenes (m-LLDPE), and combinations or copolymers thereof. According to one embodiment, the outermost liquid-tight heat-sealable layer is an LDPE, while the innermost liquid-tight heat-sealable layer is a combined composition of m-LLDPE and LDPE for optimal layering and heat-sealing properties.

The same thermoplastic polyolefin-based materials listed for the outermost and innermost layers, and in particular polyethylenes, are also suitable for inner bonding layers of the laminated material, i.e., between a main or core layer, such as paper or cardboard, and a barrier film or sheet. In one embodiment, the thermoplastic bonding layer can be a polyethylene layer, such as a low-density polyethylene (LDPE) layer.

In a further embodiment, the innermost, heat-sealable, liquid-tight polyolefin layer is a prefabricated film comprising identical or similar polyolefins, as described above, for enhanced robustness of the packaging material's mechanical properties. Due to the manufacturing process in film blowing and film casting applications, and optional subsequent film orientation steps, the polymers in these films acquire properties different from those achievable from (co)extruded coated polyolefin films. This prefabricated polymer film thus contributes to the mechanical robustness of a layered packaging material and to the mechanical strength and integrity of formed and filled packaging containers made from the layered packaging material.

According to an alternative embodiment, the suitable bonding or linking layers within the laminated material, such as, for example, between the main or central layer and the barrier-coated cellulose-based substrate, or between the outer heat-sealable layer and the barrier-coated paper substrate, are also referred to as adhesive thermoplastic polymers, such as modified polyolefins, which are mainly based on LDPE or LLDPE copolymers or graft copolymers with monomeric units containing functional groups, such as carboxylic or glycidyl functional groups, e.g. (meth)acrylic acid monomers or maleic anhydride (MAH) (i.e. ethylene-acrylic acid (EAA) copolymer or ethylene-methacrylic acid (EMAA) copolymer), glycidyl ethylene(meth)acrylate copolymer (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of these modified polymers or adhesive polymers are ionomers or ionomeric polymers. Preferably, the modified polyolefin is an ethylene-acrylic acid (EAA) copolymer or an ethylene-methacrylic acid (EMAA) copolymer.

A layered packaging material manufactured according to the above provides good integrity when transformed into loaded packaging containers, through good adhesion between adjacent layers within the layered construction and by providing good quality barrier liner and barrier pre-liner, both individually and in combination. Especially for packaging liquids and moist foods, it was an important conclusion that the adhesion between layers within the layered packaging material, as well as the barrier properties to gaseous oxygen, would also be maintained under wet packaging conditions.

According to a further embodiment, the packaging container formed from the layered packaging material can be partially sealed, filled with liquid or semi-liquid food and subsequently sealed by sealing the packaging material to itself, optionally in combination with a plastic opening or top of the container.

In conclusion, robust and reliable packaging for liquid food products can be obtained for long shelf life and storage using the barrier-coated cellulose-based substrate and the layered packaging material comprising it, as defined by the invention, thanks to the enhanced barrier properties provided. The structure of the layered packaging material performs better for forming packages by folding, both due to the improved adhesion between the substrate and the barrier material coatings and the enhanced contribution to the gas barrier properties of the barrier-coated substrate itself. This enhanced contribution is likely due to the improved combined cohesion and adhesion of the pre-coatings and barrier coating layers on the barrier-coated cellulose-based substrate.

Examples and description of preferred embodiments

The following describes preferred embodiments of the invention with reference to the drawings, of which:

Fig. 1 schematically shows a cross-section of a cellulose-based substrate coated with a barrier according to the invention,

Fig. 2a shows a schematic cross-sectional view of a layered packaging material according to the invention, comprising the barrier-coated cellulose-based substrate of Fig. 1,

Fig. 2b shows a schematic cross-sectional view of an additional layered packaging material comprising the barrier-coated cellulose-based substrate of Fig. 1,

Fig. 3a schematically shows a method for dispersion coating of a base coat or barrier pre-coat composition onto a cellulose-based substrate.

Fig. 3b schematically shows a method for the molten (co)extrusion coating of one or more layers of a heat-sealable, liquid-tight thermoplastic polymer onto a strip-shaped substrate to form the innermost and outermost layers of a packaging laminate of the invention.

Fig. 4a shows a simplified view of a plant for physical vapor deposition (PVD) coating, using a solid metal evaporation piece, onto a substrate film,

Fig. 4b shows a simplified view of a plant for plasma-enhanced chemical vapor deposition (PECVD) coating, using a magnetron plasma, on a substrate film,

Figures 5a, 5b, 5c and 5d show typical examples of packaging containers produced from the layered packaging material according to the invention, and

Fig. 6 shows the principle of how these packaging containers are manufactured from packaging laminate in a continuous “roll-to-roll” feeding, forming, loading, and sealing process.

Examples

Example 1

Two different paper substrates of the type suitable for greaseproof wraps were coated with base-layer pre-coatings and/or barrier pre-coating layers on a small pilot scale, as shown in Table 1, without an additional metallized aluminum barrier coating applied over the barrier pre-coating. The coated paper substrates were then layered into layered packaging structures as follows:

//Outer face 12 g/m2 LDPE/ Duplex CLC 80 mN, 200 g/m2, cardboard main layer / 3-4 g/m2 PVAc aqueous adhesive / barrier pre-coating paper (as listed in Table 1) / 6 g/m2 EAA adhesive polymer / 22 g/m2 inner heat-sealing layer of a combination of LDPE and m-LLDPE//

Duplex CLC board was a conventional clay-coated board, and m-LLDPE was a metallocene-catalyzed linear low-density polyethylene. The barrier-coated face of the paper substrate faced inward in the laminated structure (corresponding to the inside of a packaging container made from the laminated material). The EAA adhesive polymer and the innermost heat-sealable layer were co-extruded onto the barrier-coated paper, and the outermost LDPE layer was extruded onto the outer face of the board. The main board layer was laminated to the barrier-coated paper by wet lamination with an aqueous adhesive comprising a small amount of poly(vinyl acetate) without any intermediate drying steps.

Oxygen transmission measurements were performed with an Oxtran Mocon 2/21 device (a device based on coulometric sensors) at 23°C and at 50% and 80% RH (relative humidity), respectively, and the measured values were presented in cc/m2, for 24 hours, at 1 atmosphere of 100% gaseous oxygen (air at 1 atm that has only 20% gaseous oxygen).

Paper A was a greaseproof paper with a dense and compact surface, from Nordic Paper, identified as "Super Perga® WS Parchment" which has a basis weight of 38 g/m2.

Paper B was an anti-grease paper from Arjo Wiggins, called "Clearpack", which has a basis weight of 46 g/m2.

The papers were measured to have a surface roughness on the upper face, i.e., the face that will be coated with a barrier, of approximately 200-300 ml/min Bendtsen and approximately 150 ml/min Bendtsen, respectively.

The respective papers were thus coated only with layers of base coat and/or barrier precoat according to Table 1, i.e., with dispersion-coated precoat layers, and were then layered into the same structure as the layered packaging material. The precoating operations, as well as the layering operations to produce layered packaging material structures from the precoated papers, were carried out at pilot scale, and oxygen transmission measurements were performed on the resulting flat samples of packaging material.

Table 1

The barrier papers listed in Table 1 were thus layered either uncoated or coated with a dispersion (this type of coating method is generally known as "liquid film coating," applicable to the barrier pre-coating of dispersions or aqueous polymer solutions at low dry weights onto a substrate) in the standardized layered packaging material structure described above. The base coat pre-coatings and barrier pre-coatings were applied in 1–3 stages as listed, at a dry coating weight of approximately 1 g/m² each, with intermediate drying stages between each coating. Two types of dispersions and/or aqueous solutions were used: a natural potato starch aqueous dispersion from Avebe's Solvicol® brand, and a polyvinyl alcohol (PVOH) solution from Kuraray with a degree of hydrolysis of at least 98%, namely Poval® 6-98. When applying a starch precoat in combination with a PVOH precoat to form a barrier-coated paper, the starch coating is applied as a first basecoat, dried in an in-line dryer, and then overcoated with an additional PVOH barrier precoat, further dried, and subsequently in an in-line dryer in a second drying stage. The dispersions were applied by a gravure coating method on pilot-scale equipment, and the dry matter content of the aqueous PVOH dispersion was approximately 15% by weight. The surface temperature of the substrate in each drying operation was regulated to approximately 60 to approximately 80°C.

The dry matter content and viscosity of the starch dispersion were selected so that the low amount of starch dry matter could be applied using a gravure coating process at industrial speed. The base coat pre-coat was applied as a rich, highly adherent, dense, and homogeneous base coat to allow for the subsequent application of a small, uniform amount of the barrier dispersion pre-coat. The resulting uniform and smooth surface of the dried barrier pre-coat then allows for the application of an additional high-quality vapor deposition coating, which is consistent, homogeneous, non-porous, and highly adherent to the surface of the dried barrier pre-coat.

According to this, the coatings were applied in 2-3 consecutive coating stages, up to a dry matter weight of approximately 1 g/m2 at each coating stage, with drying of each applied coating between coating stages.

It can be concluded from the sample layered materials comprising the paper substrate pre-coated with a base coat and/or pre-coated with barrier coatings as per Table 1 that one or two starch coatings alone improve the oxygen barrier properties to some degree in each of the pre-coated papers in a layered material. However, the improvement is greater in the case of Paper A, which had a higher initial surface roughness and exhibited lower inherent oxygen barrier properties when layered in the multi-layered structure. The pre-coated papers with two or three PVOH coatings alone have more improved barrier properties than the papers with starch-only coatings, partly because starch inherently contributes less to the barrier properties of gases. However, a further significant improvement was observed when the two types of precoats were combined in the order defined by Samples 7 and 14: a first starch basecoat precoat followed by a second PVOH barrier precoat. This unexpected additional improvement in the oxygen barrier resulting from the final lamination was even more pronounced when using Paper B, the paper with the greatest smoothness and superior inherent barrier properties. Furthermore, the OTR of Sample 14 was reduced by an even greater 50% compared to Samples 12-13, where only the superior barrier precoat PVOH layers were applied.

Example 2

In addition, further barrier coating experiments were performed on the two paper types A and B in a more complete production run, as listed in samples 7 and 14 in Table 1. The papers thus pre-coated with a barrier coating, with a first base coat and a second barrier coating, were metallized and subsequently layered in the same manner into multi-layered packaging material structures. The speed of the dispersion coating operations was 400 to 600 m/min, and the coatings were applied in two consecutive coating stages, to a dry matter weight of approximately 1 g/m² each, with drying of each applied coating between stages. As in Example 1, drying was carried out at a substrate surface temperature of approximately 60 to approximately 80°C. In a separate subsequent coating operation, barrier coatings were applied by metallization over the barrier pre-coating by physical vapor deposition to an optical density of approximately 2.0, as measured by a light transmission densitometer, and a thickness of approximately 40 nm.

Samples of packaging laminate were also prepared from pre-coated paper substrates, which do not have the aluminum metallization coating applied.

The results of this experiment are listed in Table 2.

Table 2

Based on full-scale experiments, the present inventors observed an additional improved oxygen barrier (reduced oxygen transmission) in the sample corresponding to Sample 7 in Table 1, i.e., from the barrier pre-coatings on Paper A, and in Sample 14, i.e., from the barrier pre-coatings on Paper B, by means of an additional metallization overcoating. See Sample 2.3 compared to Samples 2.5 and 2.6 for Paper A, and Samples 2.1 and 2.2 compared to Sample 2.4, which refers to Paper B.

The coating speed was not perceived to significantly influence the resulting OTR measurements, as the amount of dry weight of coating applied was adjusted to approximately 1 g/m² at each different speed. Therefore, different coating operations at industrial speeds such as 400–600 m/min were not perceived to pose any problems with coating quality or effectiveness.

As can be seen from the OTR measurements at 80% relative humidity for the laminated samples that also included the metallized coating, the effect of the different contributions from the various paper qualities and the potential variations in the metallized coatings stabilizes, and the oxygen barrier results appear to end up at the same high level (i.e., the same low OTR values), thanks to the synergy between the combination of the base coat pre-coat, the barrier pre-coat, and the metallized barrier coating. Some differences in water vapor transmission values were observed, and these are believed to be due to the differences in the quality and thickness of the metallized barrier coatings in the different laminated configurations. Comparing the OTR values of the laminated samples with and without metallization barrier coating on the pre-coated paper substrate at 80% relative humidity, which is the most realistic environment for a tetrabrik-type packaging container for loaded liquid foods, there is thus a 4-5 times improvement in the oxygen barrier of the laminated packaging materials that have the specific combination of a base layer pre-coating, a barrier pre-coating and a barrier deposition coating.

Layered packaging materials, such as those produced with the configuration shown in sample 2.3 in Table 2, were further evaluated in tests on similar loading machines for forming, loading, and sealing into a loaded package. No significant problems were identified regarding packaging integrity (i.e., airtightness of the package against the surrounding environment) and sealing properties during the tests, which were therefore considered satisfactory.

Furthermore, similar barrier paper laminate structures were evaluated in the same tests, with the only difference being the laminate configuration. These laminates had a pre-made blown polyethylene film on the inside, comprising at least a partial layer with a higher proportion of linear low-density polyethylene (LLDPE). This film constitutes the innermost heat-sealable layer applied to the interior of the barrier-coated paper. Based on the results and observations from the test evaluations, it was concluded that laminate configurations with this pre-made heat-sealable film on the inside would be advantageous for further enhancing the robustness of the laminated packaging material.

Furthermore, with regard to the attached figures:

Figure 1 shows a cross-section of an embodiment of a barrier-coated paper substrate 10 of the invention. The paper substrate 11 is Nordic Paper Super Perga WS Plus greaseproof paper with a basis weight of 38 g/m², provided with a first starch-based pre-coating 12, Solvicol® from Avebe, which was applied by aqueous dispersion coating and subsequently heat-dried to evaporate the water. The dry weight of the starch-based pre-coating is approximately 1 g/m². In addition, the paper substrate has a second PVOH barrier pre-coating 13, Poval® 6-98 from Kuraray, applied over the surface of the first base-coating. The barrier pre-coating 13 was also applied by aqueous dispersion coating and subsequently heat-dried to evaporate the water. The dry weight of the PVOH barrier precoat is approximately 1 g/m2. In addition, the pre-coated barrier paper substrate has an aluminum barrier coating 14, i.e., an aluminum-metallized layer, applied over the dried surface of the barrier precoat 13, by physical vapor deposition, to an OD of approximately 2, and a thickness of approximately 40 nm.

Figure 2a shows a laminated packaging material 20a for Tetra Pak packaging of liquids, wherein the laminated material comprises a main cardboard layer 21a, having a bending strength of 80 mN and a basis weight of approximately 200 g/m², and further comprising an outer liquid-tight, heat-sealable polyolefin layer 22a applied to the outer face of the main layer 21a, which face outwards from a packaging container produced from the laminated packaging. The layer 22a is transparent to show the printed decorative pattern 27a, applied to the main paper or cardboard layer, to the outer face, thus informing consumers in retail outlets and grocery stores about the contents of the package, the packaging brand, and other information. The outer layer 22a polyolefin is a conventional, heat-sealable linear low-density polyethylene (LDPE), but may also include additional similar polymers, including LLDPE. It is applied at a rate of approximately 12 g/m². An inner, liquid-tight, heat-sealable layer 23a is positioned on the opposite side of the main layer 21a, facing the interior of a packaging container produced from the packaging laminate; that is, layer 23a will be in direct contact with the packaged product. The innermost heat-sealable layer 23a, which forms strong transverse heat seals of a liquid packaging container made of the layered packaging material, comprises one or more polyethylenes selected from the groups consisting of LDPE, linear low-density polyethylene (LLDPE), and LLDPE produced by polymerizing an ethylene monomer with a C4-C8, more preferably C6-C8, α-olefin alkylene monomer in the presence of a metallocene catalyst, i.e., so-called metallocene LLDPE (m-LLDPE). It is applied in an amount of approximately 22 g/m².

The main layer 21a is laminated to the uncoated face of the barrier-coated paper substrate 10, i.e., 25a, in Fig. 1, by means of an intermediate bonding layer 26a of low-density polyethylene (LDPE). The intermediate bonding layer 26a is formed by molten extrusion as a thin polymer melt curtain between the two paper webs, thus laminating the main layer and the barrier-coated paper substrate as the three layers pass through a contact line of cooled pressure rollers. The thickness of the intermediate bonding layer 26a is 12–18 g/m², or 12–15 g/m².

The innermost heat-sealable layer 23a may consist of one layer or alternatively two or more partial layers of the same or different types of LDPE or LLDPE or combinations thereof, and is well bonded to the surface 14 of the metallized barrier coating of the barrier paper substrate 10 by means of an intermediate coextruded bonding layer, e.g. of ethylene-acrylic acid (EAA) copolymer, thereby bonding the innermost heat-sealable layer or layers to the barrier-coated paper substrate 10 by applying the layers together in a single melt-coextrusion coating stage.

Figure 2b shows a different laminated packaging material 20b of the invention for Tetra Pak packaging of liquids, wherein the laminated material comprises a central cardboard layer 21b, having a bending strength of 80 mN and a basis weight of approximately 200 g/m², and further comprises an outer, liquid-tight, heat-sealable polyolefin layer 22b applied to the outer surface of the main layer 21b, which face the outer surface of a packaging container produced from the laminated packaging. The polyolefin of the outer layer 22b is a conventional, heat-sealable-grade low-density polyethylene (LDPE) applied at a density of 12 g/m², but may include additional similar polymers, including LLDPE. An innermost, liquid-tight, heat-sealable layer 23b is disposed on the opposite face of the main layer 21b, which is to face inwards into a packaging container produced from the packaging laminate; i.e., layer 23b will be in direct contact with the packaged product. This innermost, heat-sealable layer 23b, which will form strong heat seals of a liquid packaging container made from the laminated packaging material, comprises one or a combination of polyethylenes selected from the groups consisting of LDPE, linear low-density polyethylene (LLDPE), and LLDPE produced by polymerizing an ethylene monomer with a C4-C8, more preferably C6-C8, α-olefin alkylene monomer in the presence of a metallocene catalyst, i.e., so-called metallocene LLDPE (m-LLDPE).

The main layer 21b is laminated to the barrier-coated paper substrate described in Fig. 1 by wet lamination with an intermediate bonding layer 26b of adhesive polymer. This bonding is obtained by applying an aqueous dispersion of a poly(vinyl acetate) adhesive to one of the surfaces to be bonded together and then pressing them together on a roller contact line. This lamination step is carried out in a cold lamination or efficient ambient setting at industrial speed without any energy-consuming drying operation required to accelerate water evaporation. The dry amount of bonding layer 26b applied is only 3 to 4 g/m², which explains why drying and evaporation are unnecessary.

Thus, the amount of thermoplastic polymer can be significantly reduced in this layering layer, compared to the conventional melt-extruded polyethylene bonding layer described in Fig. 2a.

Alternatively, the innermost heat-sealable, liquid-tight layer 23b may consist of a prefabricated blown film comprising LDPE or LLDPE polymers in any combination thereof, and may be laminated to the barrier-coated paper substrate, to the surface of its barrier coating, i.e., aluminum metallization, by means of an intermediate melt-extruded laminated bonding layer 24b comprising a thicker EAA bonding layer than that used in Fig. 2a, or a simpler LDPE bonding layer, having a thickness of 12 to 20 gm, such as 12 to 18 gm.

In an alternative embodiment, the prefabricated blown film 23b' is laminated to the metallized coating by means of another wet lamination stage, with an aqueous adhesive of an adhesive layer 24b' of acrylic (co)polymer, at room temperature (cold), in an amount of 3 to 4 g/m2.

Also disclosed herein is a further embodiment, which has all the features described and a molten extruded main layer layer 26a of Fig. 2a, but is combined with the feature of an inner heat-sealable layer configuration 23b’, applied either by means of molten extrusion layering with a layer 24b, or by means of a prefabricated film, 24b’, as described in relation to Fig. 2b.

Also disclosed herein is a further embodiment in which the thin, wet adhesive aqueous dispersion layer 26a of Fig. 2b is combined with the conventional molten coextruded inner layers 24a and 23a.

Figure 3a shows an aqueous dispersion coating procedure 30a, which can be used to apply the base coat pre-coat 12 and the barrier pre-coat 13. The paper substrate strip 31a (e.g., the paper 11 in Figure 1) is fed to the dispersion coating station 32a, where the aqueous dispersion composition is applied by means of rollers onto the top surface of the substrate. If the surfaces of the two sides of the substrate are different, there is usually one side more suitable for receiving a coating or a printed decorative pattern, and this is thus the surface to be coated for this invention (often that side is called the top side or the printed side). Since the dispersion composition has a water content of 80 to 99% by weight, there will be a significant amount of water on the wet coated substrate that needs to be dried by heat and evaporated to form a continuous, homogeneous coating with uniform quality in terms of barrier and surface properties, i.e., uniformity and wettability. Drying is carried out using a hot air dryer 33a, which also allows moisture to evaporate and be removed from the substrate surface. The substrate temperature is maintained constant at 60 to 80°C as it passes through the dryer. Alternatively, drying can be partially assisted by radiant heat from infrared (IR) lamps in combination with hot air convection drying.

The resulting barrier-coated paper substrate web 34a is directed to cooling and wound onto a reel for intermediate storage and subsequent additional vapor deposition coating of a barrier deposition coating 14, onto the pre-barrier-coated paper.

Fig. 3b shows a procedure for the final layering steps in the manufacture of the packaging layer 20a or 20b, of Fig. 2a and 2b respectively, after the main layer 21a, 21b has first been layered to the barrier-coated paper substrate 10 of Fig. 1, (i.e., 25a or 25b of Fig. 2a and 2b respectively).

As explained in relation to Figs. 2a and 2b, the cardboard 21a; 21b of the main layer can be laminated to the barrier-coated paper substrate 10; 25a; 25b by means of cold and wet dispersion adhesive lamination, or by melt extrusion lamination.

The resulting paper pre-laminate web 31b is fed from an intermediate storage reel, or directly from the laminating station, to the paper pre-laminate. The unlaminated face of the main layer 21a; 21b, i.e., its printed face, is joined on a contact line 33 of cooled rollers to a curtain 32 of molten LDPE polymer, which will form the outermost layer 22a; 22b of the laminated material. The LDPE is extruded from an extruder feed block and nozzle 32b. Subsequently, the paper pre-laminate sheet, which now has layer 22a; The outermost coated layer 22b, on its printed side, passes to a second extruder feed block and a nozzle 34b and a lamination contact line 35, where a curtain 34 of molten polymer is joined and coated onto the other side of the pre-laminate, i.e., onto the barrier-coated side of the paper substrate 10; 25a; 25b. Thus, the innermost heat-sealable layer or layers 23a are co-extruded onto the inner face of the paper pre-laminate web, to form the finished laminated packaging material 36, which is finally wound onto a storage reel, not shown.

These two coextrusion stages on lines 33 and 35 of the layering roller contact can be performed alternatively as two consecutive stages in the opposite order.

According to another embodiment, one or both of the outermost layers can instead be applied at a pre-laminating station, where the co-extruded coated layer is first applied to the outer face of the main (printed) cardboard layer or over the metallization coating of the barrier-coated paper substrate, and subsequently the two pre-laminated paper bands can be joined together, as described above.

According to a further embodiment, the innermost layers of the heat-sealable, liquid-tight thermoplastic layers are applied in the form of a prefabricated film, which is laminated to the coated face of the barrier-coated paper substrate 10.

As explained in relation to Figs. 2a and 2b, this innermost layer 23a; 23 can be layered to the barrier-coated paper substrate 10 by means of wet and cold adhesive dispersion layering, or by melt extrusion layering.

Figure 4a is a simplified view of an example of a physical vapor deposition (PVD) plant for, e.g., a metallic aluminum coating on a strip substrate of the invention. The pre-coated paper substrate 44a is subjected, on its pre-coated face, to continuous evaporation deposition 40 of evaporated aluminum to form a metallized aluminum layer or, alternatively, to a mixture of oxygen and aluminum vapor to form a deposited aluminum oxide coating. The coating is provided with a thickness of 5 to 100 nm, preferably 10 to 50 nm, so that the barrier-coated paper 43 of the invention is formed. The aluminum vapor is formed from ion bombardment of a solid piece of aluminum 41 by evaporation from a source. For the aluminum oxide coating, some gaseous oxygen can be injected into the plasma chamber through inlet gates.

Figure 4b is a simplified view of an example of a plasma-enhanced chemical vapor deposition (PECVD) coating plant for, e.g., hydrogenated amorphous diamond carbon coatings on a web substrate of the invention. The web substrate 44b is subjected, on one of its surfaces, to continuous PECVD from a plasma 50 in a plasma reaction zone created in the space between the magnetron electrodes 45 and a cooled web transport drum 46, which also acts as an electrode, while the film is advanced by the rotating drum through the plasma reaction zone along the circumferential surface of the drum. The plasma for the deposition coating of an amorphous DLC coating can be created, for example, by injecting a precursor gaseous composition comprising a gaseous organic hydrocarbon, such as acetylene or methane, into the plasma reaction chamber. Other gas barrier coatings can be applied using the same main PECVD method, such as silicon oxide coatings, SiOx, starting from a precursor gas of an organosilicon compound.

Figure 5a shows an embodiment of a packaging container 50a produced from a packaging laminate according to the invention. The packaging container is particularly suitable for beverages, sauces, soups, or similar products. Typically, this container has a volume of approximately 100 to 1000 ml. It can be of any configuration, but preferably has a Tetra Pak shape, having longitudinal and transverse seals 51a and 52a, respectively, and optionally an opening device 53. In another embodiment, not shown, the packaging container can be shaped like a wedge. To obtain this "wedge shape," only the lower part of the container is formed by folding so that the transverse heat seal of the bottom is concealed under triangular corner tabs, which are folded and sealed against the bottom of the container. The transverse seal of the upper section is left unfolded. Thus, the packaging container, only partially folded, is still easy to handle and dimensionally stable enough to place on a shelf in the food warehouse or on any flat surface.

Figure 5b shows an alternative example of a packaging container 50b produced from an alternative packaging laminate according to the invention. The alternative packaging laminate is thinner, having a thinner main layer, and is therefore not dimensionally stable enough to form a parallelepiped or wedge-shaped packaging container, and does not fold after transverse sealing 52b. The packaging container will remain a pillow-shaped pouch-type container and will be distributed and sold in this form.

Figure 5c shows a 50c container with a gable lid, formed by folding a pre-cut blank or sheet from the laminated packaging material comprising a main layer of cardboard and the barrier-coated paper substrate of the invention. In addition, containers with a flat top can be formed from similar blanks.

Figure 5d shows a bottle-type container 50d, which is a combination of a sleeve 54 formed from pre-cut blanks of the laminated packaging material of the invention and a top portion 55, formed by injection molding plastics in combination with an opening device such as a screw cap or the like. This type of container is marketed, for example, under the trade names Tetra Top® and Tetra Evero®. These particular containers are formed by joining the molded top portion 55 with an opening device attached in a closed position to a tubular sleeve 54 of the laminated packaging material, sterilizing the cap of the top portion of the bottle thus formed, filling it with the food product, and finally forming the bottom portion of the container by folding and sealing it.

Figure 6 illustrates the principle described in the introduction of this application, namely, a band of packaging material is formed in a tube 61 by overlapping the longitudinal edges 62, 62' of the band and heat-sealing them together to form an overlapping seam 63. The tube is continuously filled 64 with the liquid food product to be filled and divided into individual filled packages by repeated double transverse seals 65 of the tube at a predetermined distance from each other below the level of the contents filled into the tube. The packages 66 are separated by cutting between the double transverse seals (upper and lower seals) and are finally shaped into the desired geometric configuration by folding along pre-formed fold lines in the material.

As a final observation, the invention is not limited to the embodiments shown and described above, but may be varied within the scope of the claims.

Claims (18)

1. A barrier-coated cellulose-based substrate (10) for use as a barrier film in a layered packaging material for liquid food products, comprising a cellulose-based substrate (11) and, applied on a first face of the cellulose-based substrate, a barrier pre-coating (13) applied by means of a dispersion or solution coating, and further, on the barrier pre-coating, a barrier coating (14) applied by vapor deposition, the barrier coating being applied by means of a vapor deposition method, wherein the barrier-coated cellulose-based substrate (10) further comprises a base layer pre-coating (12), which is different from the barrier pre-coating (13) and is applied by means of a dispersion or solution coating onto the cellulose-based substrate (11) and is thus directly adjacent to and in contact with the first face of the cellulose-based substrate layer, and is located below the barrier pre-coating, the Cellulose-based substrate coated with a barrier suitable for providing barrier properties to gases and water vapor in a laminated packaging material and packaging made from it. 2. Cellulose-based substrate (10) coated with a barrier according to claim 1, wherein the barrier pre-coating (13) comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of poly(vinyl alcohol), PVOH, and ethylene-vinyl alcohol, EVOH. 3. Cellulose-based substrate coated with a barrier according to any one of claims 1-2, wherein the barrier pre-coating (13) has been applied by means of coating with dispersion or solution in an amount of 0.5 to 2 g/m2, preferably 0.5 to 1.5 g/m2, dry weight. 4. Cellulose-based substrate coated with a barrier according to any one of claims 1-3, wherein the barrier coating (14) is a vapor deposition coating of a material selected from metals, metal oxides, inorganic oxides and carbon coatings. 5. Cellulose-based substrate coated with a barrier according to any one of claims 1-4, wherein the barrier coating (14) is a vapor deposition coating selected from the group consisting of an aluminum metallization coating, and aluminum oxide, AlOx, and preferably an aluminum metallization coating. 6. Cellulose-based substrate coated with a barrier according to any one of claims 1-5, wherein the barrier coating (14) is applied by deposition to a thickness of 10 to 80 nm, such as 10 to 50 nm, such as 10 to 45 nm. 7. Cellulose-based substrate coated with a barrier according to claim 5, wherein the barrier deposition coating (14) is an aluminum metallization coating, which is applied to an optical density OD of 1.8 to 2.5, as measured herein. 8. Cellulose-based substrate coated with a barrier according to any one of the preceding claims, wherein the base layer pre-coating (12) comprises a polymer selected from the group consisting of starch, modified starch, and cellulose ethers. 9. Cellulose-based substrate coated with a barrier according to any one of the preceding claims, wherein the base layer pre-coating (12) comprises a material selected from the group consisting of starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose CMC, hydroxyethylcellulose HEC, hydroxypropylcellulose HPC, hydroxypropylmethylcellulose HPMC, and sodium carboxymethylcellulose NaCMC. 10. Cellulose-based substrate coated with a barrier according to any one of the preceding claims, wherein the base layer pre-coating (12) has been applied by means of coating with dispersion or aqueous solution and in an amount of 0.5 to 2 g/m2, preferably 0.5 to 1.5 g/m2, dry weight. 11. Layered packaging material (20a; 20b) comprising the cellulose-based substrate (10; 25a; 25b) coated with a barrier according to any one of claims 1-10, and further comprising a first outermost protective layer (22a; 22b) and a second innermost liquid-tight heat-sealable layer (23a; 23b; 23b'). 12. Layered packaging material (20a; 20b) according to claim 11, wherein the second innermost liquid-tight heat-sealable layer (23a; 23b; 23b') comprises a polyolefin polymer. 13. Laminated packaging material (20a; 20b) according to any one of claims 11-12, further comprising a main layer (21a; 21b) of paper or cardboard or other cellulose-based material, and, disposed on the inner face of the main layer of paper or cardboard, between the main layer and the innermost second layer (23a; 23b; 23b') of liquid-tight heat-sealable material, said barrier-coated cellulose-based substrate (10; 25a; 25b). 14. Layered packaging material (20a; 20b) according to claim 13, wherein the barrier-coated cellulose-based substrate (10; 25a; 25b) is bonded to the main layer (21a; 21b) by an intermediate bonding layer (26a; 26b) comprising a composition comprising a binder selected from the group consisting of acrylic polymers and copolymers, starch, cellulose derivatives and polysaccharides, vinyl acetate polymers and copolymers and/or vinyl alcohol. 15. Layered packaging material (20a; 20b) according to any one of claims 12-14, wherein the second (23a; 23b; 23b') innermost liquid-tight heat-sealable polyolefin layer is a prefabricated film comprising the same or similar polyolefins for an improvement of the robustness of the mechanical properties of the packaging material. 16. Packaging container (50a; 50b; 50c; 50d) comprising the layered packaging material defined in any one of claims 11-15. 17. Method for manufacturing a barrier-coated cellulose-based substrate (10; 25a; 25b; 44a) according to any one of claims 1-10, comprising a first step of providing a cellulose-based substrate as a moving belt (31a) in a roller feeding system, a second stage of coating with a dispersion (liquid film coating) (32a) a first dispersion or solution of a basecoat precoat composition onto the mobile cellulose-based substrate (31a), and subsequently drying (33a) the applied basecoat precoat by forced evaporation, a third step of coating with dispersion (32a') a second dispersion or solution of a barrier precoat composition having different ingredients than the basecoat precoat composition onto the mobile cellulose-based substrate coated with basecoat (31a'), and subsequently drying (33a') the applied barrier precoat by forced evaporation, and a fourth step of additionally depositing (40) onto the barrier pre-coating of the cellulose-based substrate (43) pre-coated with a mobile barrier by means of a vapor deposition coating operation (41). 18. Method according to claim 17, wherein the base coat pre-coating composition (12) is an aqueous dispersion of a material selected from the group consisting of starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose CMC, hydroxyethylcellulose HEC, hydroxypropylcellulose HPC, hydroxypropylmethylcellulose HPMC, and sodium carboxymethylcellulose NaCMC.